The primary objective of this research program is to study mechanisms of immunocyte differentiation, antigen recognition, and T-cell B-cell, macrophage T-cell interaction in humoral and cellular immune responses. This objective will be accomplished through our continued investigation of the relationship of these immunologic functions to histocompatibility linked immune response gene products - Ia antigens. Antibodies produced in mice and reactive with Ia antigenic determinants will be used to determine whether Ia membrane structures are critical to these immune mechanisms. Anti-Ia serum will be used to block membrane determinants and anti-Ia serum with complement will be used to prepare populations of lymphoid cells depleted of specific Ia positive cells.